1. Field of the Invention
The present invention relates to a hard magnetic alloy having excellent magnetic characteristics and temperature-dependent properties and used in sensors such as magnetic encoders and potentiometers, motors, actuators, and speakers. The present invention relates to a hard magnetic alloy compact and a method for producing the alloy and the compact.
2. Description of the Related Art
Nd-Fe-B magnets and Sm-Co magnets are generally known as magnetic materials which show superior characteristics to that of ferrite magnets and Alnico (Al-Ni-Co-Fe) magnets. Novel alloy magnets having further improved characteristics and particularly Sm-Fe-N magnets have also been intensively studied. These magnets, however, must contain at least 10 atomic % of Nd or at least 8 atomic % of Sm. Use of large quantities of expensive rare earth elements inevitably increases the production costs. Since the magnetic characteristics of Nd-Fe-B magnets are largely dependent on temperature, they cannot be used as sensors. On the other hand, Sm-Co magnets have not been used in practice in spite of their smaller thermal coefficients of magnetization, because they are more expensive than the Nd-Fe-B magnets.
Ferrite magnets and Alnico magnets are inexpensive compared to the rare earth magnets; however, the ferrite magnets have larger thermal coefficients of magnetization and thus cannot be used as sensors, whereas the Alnico magnets have extremely low coercive forces.
The above-mentioned hard magnetic alloys have been produced by spraying molten alloys onto rotating drums to form thin ribbons by quenching the alloys or by spraying molten alloys into cooling gas to form alloy powders by quenching alloy droplets. The thin ribbons and alloy powders must therefore be formed into given shapes before being used for motors, actuators, and speakers.
Typical methods for molding magnetic powder include compaction molding and injection compacting of a mixture of the magnetic powder and a rubber or plastic binder. The resulting magnet is referred to as a "bond magnet". Since the versatility of possible form features of bond magnets is high, they have been widely used in electronic parts. The binder in bond magnets, however, causes inferior magnetic characteristics because of decreased remanent magnetization and low mechanical strength of the bond magnet.
Accordingly, the advent of inexpensive magnetic materials having hard magnetic characteristics superior to those of ferrite magnets and excellent temperature-dependent properties has been eagerly awaited.
The present inventors have studied inexpensive hard magnetic materials having excellent magnetic characteristics and temperature-dependent properties, and have discovered from various experimental results that the thermal coefficient of magnetization is related to the permeance factor p.
Also, the present inventors have directed their attention to the heating rate during annealing of a quenched alloy essentially consisting of an amorphous phase and discovered that hard magnetic characteristics are related to the nano-crystalline structure (particularly, crystal grain size of the bcc(body centered cubic)-Fe phase) in a fine crystalline phase which is precipitated by the annealing.